New string partition functions with vanishing cosmological constant

We present a series of new one-loop nonsupersymmetric four-dimensional heterotic-string partition functions that we conjecture to lead to vanishing one-loop cosmological constants. We demonstrate that our partition functions satisfy various requirements imposed by the physical consistency of possible underlying string models, and we discuss the results of an automated search for such models. Although we find no such models directly, we surprisingly discover many sets of models whose partition functions algebraically differ precisely by our expressions. These models thus represent new and unexpectedly degenerate points in the space of string-field-theory vacua.